To facilitate the understanding and description of the present invention as well as the knowledge of the problems behind the invention, here follows a description of both the basic construction and the function of floor panels with reference to FIGS. 1-6 in the accompanying drawings. This basic construction and function is also completely or in parts used in the present invention.
A mechanical locking system comprises a tongue and a tongue groove for vertical locking and a locking element and a locking groove for horizontal locking. It has at least four pairs of active cooperating locking surfaces, two pairs for vertical locking and two pairs for horizontal locking. The locking system comprises several other surfaces, which generally are not in contact with each other and can therefore be produced with considerably larger tolerance then the cooperating locking surfaces.
Laminate floorings are usually composed of a core consisting of a 6-9 mm fiberboard, a 0.20 mm thick upper surface layer and a lower balancing layer. The surface layer provides appearance and durability to the floor panels. The core provides stability and the balancing layer keeps the board level when the relative humidity (RH) varies during the year.
The mechanical locking systems are generally formed by machining the core of the board. Such machining must be very precise in order to ensure a high quality. It is especially important that the cooperating vertical and horizontal locking surfaces are formed with high precision in order to ensure easy installation and a precise fit between adjacent edges.
FIG. 1a illustrates according to prior art a mechanical locking system (strip lock), which can be locked with angling and which is widely used on the market. Such a locking system can also be designed to be locked with vertical or horizontal snapping. A vertical cross section of the floor panel is shown of a part of a long side 4a of the floor panel 1′, as well as a part of a long side 4b of an adjoining floor panel 1. The bodies of the floor panels 1, 1′ can be composed of a fiberboard body or core 30, which supports here, a wear resistant and decorative surface layer 31 on its front side and a balancing layer 32 on its rear side (underside). The locking system has a tongue 10 and a tongue groove 9 which locks the panels in a vertical direction D1 with upper 53 and lower 56 tongue surfaces that cooperate with upper 43 and lower 46 tongue grooves surfaces. A strip 6 is formed from the body and balancing layer of the floor panel and supports a locking element 8 on a locking element side 1. Therefore the strip 6 and the locking element 8 in a way constitute an extension of the lower part of the tongue groove 46. The locking element 8 formed on the strip 6 has an operative locking element surface 11 which cooperates with an operative locking groove surface 12 in a locking groove 14 in the opposite locking groove side of the adjoining floor panel 1′. By the engagement between the horizontal operative locking surfaces 11, 12 a horizontal locking of the floor panels 1, 1′ transversely of the joint edge (direction D2) is obtained if the panels are pulled apart. The locking angle A of the locking surfaces 11, 12 is in this shown embodiment 90 degrees and this gives a very strong horizontal locking. Locking systems are also formed with other locking angles for example 45-60 degrees. Some locking systems have a very low locking angle for example 30 degrees. Low locking angles makes it possible to make very compact locking systems and to save material. The locking strength of such systems is however very low. The upper part of the locking element side 1 comprise a first upper edge 19 and the upper part of the locking groove side 1′ comprises a second upper edge 18 that are preventing a horizontal movement if the panels are pressed together.
FIG. 1b shows a laminate surface layer, which consist of a transparent overlay 33 with wear resistant particles of aluminum oxide 36, and a decorative paper layer 35 with a print 34 giving the surface its decorative properties. The print, which in most cases is a wood design, has generally a white base layer, which is not visible in a floor panel with straight and vertical upper edges. Some floor panels are formed with decorative bevels 31a, which are covered with paint or a decorative tape. It is also known that a part of the overlay 31b can be machined as a small bevel in order to make the edge softer and to remove edge chipping which can occur if the tools are not sharp. Such a machining of the overlay is made as a final step after the machining of the surface layer and the upper edge with processes similar to sanding operations.
A locking system (tongue lock) can also be formed without a strip 6 as shown in FIG. 2a. The locking element 8 is in this embodiment located on the tongue 10 and the locking groove 14 is formed as an undercut groove in the tongue groove 9.
A locking system can also be formed with a flexible tongue 10a (fold lock), which can be displaced during locking. Such a locking system, as shown in FIG. 2b, can be locked with a vertical movement D1.
A locking system (hook lock) can also be formed without a tongue, as shown in FIG. 2c, in order to lock only in the horizontal direction D2. Such a locking system is used on the short sides of narrow floor panels. The vertical locking is accomplished with the long sides of adjacent panels.
All of these known locking systems, which are used to lock panels horizontally, have two pairs of cooperating surface 18, 19 and 11, 12, which must match each other in a precise manner in order to work properly.
FIGS. 3a (side view) and 3b (top view) illustrate the most used method to produce a locking system and the main problems related to such production. The locking system is formed with the surface 31 of the floor panel pointing downwards. Several rotating tool configuration 60 are used to profile the edges when a floor panel 1, 1′ is displaced horizontally in a linear feeding direction by a chain 70. A belt 70a supported by pressing wheels 70b is used to create a vertical pressure against the chain. The belt has no stability in the horizontal D2 direction perpendicularly to the feeding direction. The vertical D1 and horizontal position D2 of the floor panel is obtained by the chain, which moves with high precision in relation to the rotating tool configuration. The surface layer of the floor panel is fixed to the chain with friction.
FIG. 4a shows a floor panel, which is produced with a profiling equipment comprising one chain 70, and one belt 70a supported by pressing wheels 70b creates a vertical pressure against the chain. FIG. 4b shows that a perfect machining can form very precise grooves 14, locking elements 8 and upper edges 18, 19, which in theory are almost completely parallel. The production tolerances can be as low as +−0.02 mm. In practice, it is however very difficult to reach such tolerances. The reason is that the friction between the chain and the floor surface is not sufficient and the floor panel is moving or turning horizontally perpendicularly to the feeding direction during the production (hereafter referred to as horizontal turning). The belt, the chains, especially if they are not parallel, the tools and pressure shoes, which also are used (not shown), creates uncontrolled horizontal side pressures against the floor panel and the above mentioned parts of the locking system will not be formed completely parallel as shown in FIG. 4c. The distances L1, L2 between the upper part of the floor panel 18, 19 and the locking surfaces 11, 12 at one part of the panel can for example be 0.1-0.2 mm smaller than the corresponding distances L3, L4 at another part of the same panel. The locking can be to tight or to loose. The tongue 10 and the tongue groove 9 can also vary in the horizontal direction. Such tolerances 10′, 9′ as shown in FIG. 1a does not cause any problems however since the locking system is formed with spaces between the tip of the tongue and the inner part of the groove and such spaces are used to compensate the above mentioned production tolerances.
Several methods have been used to solve problems related to horizontal turning. The most used methods are to make the profiling equipment more stable with improved guiding of the chains. Cleaning devices are also used to clean the chain in order to maintain high friction between the chain and the floor panel. Special guiding devices GD as shown in FIG. 4a, such as steal rulers, which cooperate with special grooves on the rear side of the panel, have been used to prevent horizontal turning. Such rulers and grooves are difficult to adjust, they create wear and heat during production and can create stability problems when a balancing layer is separated by a groove.
All these efforts to improve the profiling equipment have however not solved the problems. On the contrary the problems of horizontal movement have increased over the years. One reason is that the production speed has increased and this creates stronger side pressure. Floor panels with smaller sizes, deep surface embossing and glossy surfaces have been developed and this decreases the friction between the chain and the floor surface and increases the risk for a considerable uncontrolled horizontal turning.
Other methods, which also have been introduced, are based on the principle to use tool design and tool positions to decrease horizontal turning. This is shown in FIGS. 5 and 6.
FIGS. 5a-5e show a traditional tool setup solutions for producing floor panels with a wear resistant top surface layer. The floor panel is moving in the feeding direction FD of the arrow during the profiling of the edges. The first step in the profiling line is illustrated in FIG. 5a and the last step in FIG. 5e. The cross section of floor panel 1, 1′ is shown, positioned with the top surface layer 31 downwards on a ball bearing chain 70 in a milling machine. A traditional machining setup conveys the board 1, 1′ with great accuracy past a number of independently rotating cutting tool configurations. The cutting tools have generally a tool diameter of approximately 200-250 mm and can be set at an optional tool angle TA to the horizontal plane HP of the board. The tools are mounted on opposite sides of several columns. The distance between the tools TD is about 0.5 m and the distance between the columns CD is about 1 m as shown in FIGS. 3a and 3b. Each tool 60-64, 60′-63′ is dedicated to remove a limited part of the joint edge, where some are also forming the final joint surfaces. Several tools are positioned along both sides of the profiling line in the feeding direction FD of the floor panel 1, 1′. This is done in order to obtain sufficient production tolerances. A general rule is that an increase in number of tools result in improved production tolerances since each tool removes less material and creates lower forces that can displace the floor panel in an uncontrolled way. The normal production mode is to use 4-6 opposite tool pairs, on a first machine cutting the long side, followed by a similar machine cutting the short side locking system on the panel.
The horizontal locking surfaces 18, 19, 11, 12 are machined with four independent tools 62, 62′ and 63, 63′. A horizontal turning between the third (FIG. 5c) and the fourth (FIG. 5d) tool stations on each side will create horizontal locking surfaces 18, 19, 11, 12 which are not parallel as shown in FIG. 4c. 
Traditionally, when producing mechanical locking systems in a floor panel, rough cutting tools 60, 60′, as illustrated in FIG. 5a, or the fine cutting tools 62, 62′, as illustrated in FIG. 5c, are positioned at one independent profiling position on one side of the feeding direction FD of the floor panel 1, 1′ and on the opposite side as opposite pairs. One tool of the pair is machining the locking element side 1, and the other tool is machining the locking groove side 1′. The rough cutting tools 60, 60′ are removing the majority of the high abrasive material of the wear resistant surface layer in order to increase the lifetime and the cutting quality of the next coming tools, with the exception of tool 62, 62′ that also cut in the wear resistant surface layer. The cutting edges of the tools consist of diamond, but even so, the running time of such a tool is limited, normally not more than 5 000-20 000 meters when cutting in a high abrasive top layer. Because of this, the tools that cut the surface layer, the rough cutting tools 60, 60′, as illustrated in FIG. 5a, and the fine cutting tools 62, 62′, as illustrated in FIG. 5c are configured with a straight cutting edge that can be stepwise moved M parallel to the cutting edge during production in order to bring a fresh tool cutting edge into a cutting position.
Such a horizontal rotation with a horizontal tool angle TA and a stepwise vertical adjustment M is shown in FIGS. 6a-6c. FIG. 6a shows the chip-removing surface 71 of the fine cutting tool 62 that is forming the top surface layer 31 of the floor panel 1. If the board have a wear resistant top surface layer the fine cutting tool is worn down much faster compared to cutting in the core of the board, e.g. high density fiber board (HDF). The result is a worn down portion of the cutting surface 72 as shown in FIG. 6b on the tool 62, which results in so-called chipping of the top edge portion of the panel 73, i.e. small cracks occur and the edge becomes rough and small white portions from the base layer of the print can show. FIG. 6c illustrates how the fine cutter 62 is moved in small steps in the vertical direction M some few tenth of a millimeter, so that a fresh cutting portion 71 of the tool 62 is in position against the top surface 31. A similar principle is used for the rough cutters and the stepwise movement of the tools is done while the machine is running in order not to lose running time in the line.
The rough cutting tools 60, 60′ in FIG. 5a are generally positioned with a distance ED of approximately 0.5 mm from the vertical plane VP and from the final upper edge 18, 19. All next coming cutting tools, except the fine cutter 62, 62′ are all designed such that their cutting teeth will keep a safe distance to the surface layer in the upper edge in order to avoid the risk of cutting into the wear resistant surface layer 31 and thereby avoid that they wear down fast, especially since these tools cannot be moved stepwise.
The horizontal turning inside the profiling machine is to a large extent related to the fact that the tools create uncontrolled side pressures on the panels. Such side pressures can occur if tools work with different tool angles, different rotations (with or against the feeding direction) or if they remove different amounts of material or material with different composition (core, surface layer).
The boards 1, 1′ are generally more unstable and the risk for horizontal turning is high in the first and the last cutting position, relative to the other tool positions due to several reasons. For example the board is only clamped by the chain and the belt over a limited length and the inlet/outlet equipment may push the boards slightly.
The machining of the cooperating horizontal locking surfaces 11, 12, 18, 19 are therefore generally positioned at the inner tool positions in conjunction to each other. They are formed by fine cutters 62, 62′ in FIG. 5c and locking groove cutter 63′, locking element cutter 63 in FIG. 5d. The fine cutters 62, 62′ in FIG. 5c are generally always positioned after the tools that forms the tongue and the tongue groove as shown in FIG. 5b. This is a major advantage since a majority of the material is already removed by the previous tools 60, 60′, 61, 61′ when the fine cutters start to remove material. The fine cutters 62, 62′ must only remove a very limited amount of the core material and the last part of the wear resistant surface layer 31. This makes it possible to obtain tight machining tolerances, by reducing the cutting forces and the horizontal pressure on the floor panel.
The rough cutters 60, 60′ and the fine cutters 62, 62′ are as described above always separated with several tool positions in between. This causes a substantial uncontrolled horizontal turning between the rough cutters 60, 60′ and the fine cutters 62, 62′ and such turning can be about 0.2 mm. The rough cutters must therefore be positioned at a safe distance, generally at least 0.5 mm, from the final surface edge, in order to avoid quality problems such as chipped edges, white visible lines of décor paper and core exposure.
The locking surfaces of the locking groove 14 and locking element 8 are formed with rotating tool configuration 63, 63′ having a tool angle TA equal or larger than the locking angle LA. A rotating tool configuration forming a locking surface with a locking angle A can never work with a tool angle TA which is lower than the locking angle A. This fact is a considerable limitation, which must be considered in the design and production of the locking systems.
The horizontal and vertical locking tools 61, 61′, 63, 63′ in FIGS. 5b and 5d are all examples of a rotating tool configurations consisting of two in relation to each other adjustable tool bodies TB1 and TB2 mounted on the same shaft. Such tools are hereafter referred to as COMBI tools. These COMBI tools are needed when the tool is forming a geometry, e.g. a groove, that consist of two opposite cutting surfaces with a fixed relative distance between each other. When the tool is sharpened, then some of the material of the tool is removed and the relative distance between the opposite edges is changed. The two bodies can therefore be adjusted to an oversize dimension and then be grinded into a correct relative dimension. A positive effect of these COMBI tools are that the accuracy between the two profiled surfaces formed by the two tool bodies is very accurate since it is profiled at the same position and with the same tool. Such COMBI tools 61, 61′ can be used to improve the tolerances between a pair of the vertical locking surfaces of the tongue, as shown in FIG. 5b. COMBI tools are however not used to produce a pair of the horizontal locking surfaces. One reason is that the upper edge on the locking groove side must be formed with a tool body 62′ having a tool angle which is different to the tool angle of the tool body 63′ forming the locking surface in the locking groove as shown in FIGS. 5c and 5d. The tool bodies of a COMBI tool are always working with the same tool angle since they are fixed on the same shaft. Another reason is the fact that one of the tool bodies 62, which forms the upper edge, must work horizontally and must be adjustable stepwise vertically. A COMBI tool 63, 63′ cannot be adjusted stepwise vertically since such an adjustment will at the same time change the position of the other tool body TB1 and TB2, which is used to form the locking surface of the locking element. A COMBI tool with two tool bodies on the same shaft has therefore two major limitations. Both tool bodies TB1, TB2 must work with the same tool angle and must be displaced in the same direction at the same time.
The main challenge while machining a mechanical locking system, apart from overall production cost, is to obtain sufficient production tolerances, i.e. to get a proper geometry of the joint and to do this in a cost efficient production mode. Accordingly, it would be highly desirable in the manufacturing of floor panels to reduce the horizontal locking tolerances further to a considerably lower level and in a more cost effective and easy way.